Factors responsible for rapid dissipation of acidic herbicides in the coastal lagoons of the Camargue (Rhône River Delta, France)

This study was aimed at investigating which processes cause acidic herbicides (e.g., bentazone, MCPA and dichlorprop) to rapidly disappear in the lagoons of the Rhône delta, which are peculiar brackish and shallow aquatic environments. The use of the model MASAS (Modeling of Anthropogenic Substances in Aquatic Systems) revealed that sorption, sedimentation, volatilization, flushing and abiotic hydrolysis had a minor role in the attenuation of the investigated herbicides. Laboratory scale biodegradation and photodegradation studies were conducted to better assess the significance of these two processes in the natural attenuation of herbicides in brackish (lagoons) waters with respect to fresh waters (canals draining paddy fields). Herbicide biodegradation rates were significantly lower in lagoon water than in canal water. Consequently, photodegradation was the main dissipation route of all investigated herbicides. The contribution of indirect photolysis was relevant for MCPA and dichlorprop while direct photolysis dominated for bentazone removal. There is a need to further investigate the identity of phototransformation products of herbicides in lagoons.     

Mercury and methylmercury concentrations in high altitude lakes and fish (Arctic charr) from the French Alps related to watershed characteristics

Total mercury (THg) and methylmercury (MeHg) concentrations were measured in the muscle of Arctic charr (Salvelinus alpinus) and in the water column of 4 lakes that are located in the French Alps. Watershed characteristics were determined (6 coverage classes) for each lake in order to evaluate the influence of watershed composition on mercury and methylmercury concentrations in fish muscle and in the water column. THg and MeHg concentrations in surface water were relatively low and similar among lakes and watershed characteristics play a major role in determining water column Hg and MeHg levels. THg muscle concentrations for fish with either a standardized length of 220 mm, a standardized age of 5 years or for individualuals did not exceed the 0.5 mg kg^− 1 fish consumption advisory limit established for Hg by the World Health Organization (WHO, 1990). These relatively low THg concentrations can be explained by watershed characteristics, which lead to short Hg residence time in the water column, and also by the short trophic chain that is characteristic of mountain lakes. Growth rate did not seem to influence THg concentrations in fish muscles of these lakes and we observed no relationship between fish Hg concentrations and altitude. This study shows that in the French Alps, high altitude lakes have relatively low THg and MeHg concentrations in both the water column and in Arctic charr populations. Therefore, Hg does not appear to present a danger for local populations and the fishermen of these lakes.     

Waves in periodic layered waveguides

Analytical expressions for EM-waves and evolutionary equations for the waves in geometric regular waveguides with layered nonstationary media are presented. A piecewise-homogeneous and periodic along the guide's axis medium is considered in detail. The analytical solution of the dispersion equation is invariant to both the guide's cross-section contour form and eigenwave type. The periodicity dispersion, particular resonances and an algorythm of the modeling application are discussed.     

Effective Elastic Properties of Fractured Rocks: Dynamic vs. Static Considerations

We present a new technique for static computations of effective elastic properties of multiple fractured rocks. This approach is based on the viscoelastic rotated staggered finite-difference (FD) grid wave propagation technique. Our simulations are used to explain discrepancies of some recent numerical studies. The focus is on scale effects of a so-called representative volume element (RVE). From the point of view of classical micromechanics we review different numerical techniques: Static as well as dynamic numerical experiments. We show that the differential effective medium theory (DEM) is capable of producing satisfactory predictions of effective elastic moduli. For non-dilute crack densities this is not the case for the non-interacting approximation (NIA).     

Two‐zero four‐pole building block for microwave waveguide filters using all‐resonant modes at their cutoff frequency

This article describes a basic building block for microwave waveguide filters. It uses a new coupling scheme where all resonant modes are used at their cutoff frequency. It is composed of a cascade of basic nonloaded rectangular cavities where the modes are alternately single mode and dual mode. These cavities are coupled directly, without any iris. Neither coupling nor tuning screws are needed. The analysis of the discontinuities is performed by the method of moments (MoM). The synthesis makes use of an optimization method based on the genetic algorithm. Prototypes have been realized and measurements are shown to confirm the analysis results. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13: 429–437, 2003.     

Measurement of enthalpies of mixing in gaseous phase for the binary system carbon dioxide – hydrogen sulphide by an isothermal flow calorimeter

Enthalpies of mixing for the binary system carbon dioxide – hydrogen sulphide were measured by means of an isothermal flow calorimeter at temperatures of 293.15. 305.15 and 313.15 K. For the first isotherm, excess enthalpy measurements were made at pressures of 0.507, 1.013 and 1.419 MPa. For the last two isotherms, these measurements were performed at pressures of 0.507, 1.013 and 1.520 MPa. The experimental data were treated by the same techniques described for the systems previously studied (Barry et al., 1982a, 1982b, 1982c). Two types of binary interaction coefficients k_ij have been utilized for the prediction of experimental data from equations of state: coefficients k_ij independent of temperature and pressure, and k_ij's adjusted as function of temperature and pressure. A better prediction of the excess enthalpy experimental data was obtained from the latter series of binary interaction coefficients.     

Nouvelle méthode de traitement de séries de données tronquées dans l'étude de la pollution atmosphérique

The statistical treatment of sets of data including some values that are below the detection limit is frequently used in air pollution studies. These values are usually, and conventionally, set at one half of the detection limit. The present paper discusses the validity of this convention and shows on both theoretical and empirical grounds that it is better to set these values at two thirds rather than one half of the detection limit.